1. Field of the Invention
This invention relates to measuring and monitoring of intracranial pressure changes in human patients, and more particularly to a non-invasive method and device for monitoring changes in intracranial pressure which removes extracranial effects from the measurements.
2. Background of the Invention
A prior method of measuring intracranial pressure included pulse phase-locked ultrasonic technology but this method did not include techniques nor refinements to remove extracranial effects from the measurements.
Another prior method includes an ultrasonic means to measure expansion of a pre-selected path through the cranial cavity by means of placement of a 500 KHz ultrasonic transducer at an appropriate location on the skull. In this technique, the measurement includes not only skull expansion, but also includes effects of edema and perfusion of tissues between the skin and the skull. This perfusion can result in measurements that are much larger than the path change due to cranial vault expansion alone.
Other measurement techniques such as strain sensor gauges located on a caliper can be placed across the cranial cavity for measurement. Such techniques, however, are also subject to the same problems associated with surface tissue edema and perfusion, similar to the ultrasonic technique.
Thus, although prior devices and methods are generally non-invasive, they are affected by surface tissue changes. These changes affect the accuracy of the determination of cranial vault expansion. In the above-mentioned techniques, the effects due to surface tissue could be eliminated, but that would require the excision of tissue around the connecting points (for the strain gauge caliper) or around the transducer point-of-contact (for the ultrasonic technique). This would make the techniques invasive, although not as invasive as drilling a hole through the cranium for insertion of a probe.
The present invention overcomes these and other disadvantages of the prior art by providing an improved method and device for measuring intracranial pressure changes and including the means to improve the accuracy of measurement of intracranial expansion.
This invention is a method and device for measuring change in intracranial distances and includes calibration techniques necessary to convert these measurements to changes in intracranial pressure. It is an object of the invention to provide a non-invasive method and device for measuring change in intracranial distances which removes extracranial effects from the measurements, and to provide calibration techniques that enable that change in skull dimension to be related to the change in intracranial pressure. It is a further object to provide a non-invasive method for monitoring changes in intracranial pressure in human patients.
These and other objects of the invention are achieved by introducing known intracranial pressure changes using a non-invasive technique. The changes in skull dimension as a result of changes in intracranial pressure are then measured using a non-invasive device which removes extracranial effects (e.g., caused by changes in skin thickness and variation) from the measurement. The measured changes in skull dimension are then correlated to changes in intracranial pressure.